Advanced age is the single greatest risk factor for developing osteoarthritis (OA). Accumulating evidence points to oxidative stress, as an important factor contributing to both ageing and the development of age- related diseases like OA. Elevated levels of reactive oxygen species (ROS) have been observed in the cartilage of OA patients and may play a role in the stimulation of articular cartilage extracellular matrix (ECM) degradation. ROS have been shown to serve as secondary messengers in integrin and cytokine signaling pathways which stimulate chondrocyte production of ECM degrading enzymes called matrix metalloproteinases (MMPs). Fibronectin fragment (FN-f) stimulation of the a5[unreadable]1 integrin has been shown to increase intracellular levels of ROS in chondrocytes, while ROS inhibition blocked FN-f stimulated MMP-13 expression. However, both the source of ROS and the mechanism by which ROS mediate this integrin signaling pathway remains unclear. Thus, the objective for this proposed research is to elucidate the key redox regulated signaling events in the stimulated a5[unreadable]1 integrin pathway in chondrocytes. Our general hypothesis is that redox-regulated signaling proteins within the integrin pathway, including c-Jun N-terminal kinase 2 (JNK2), are targeted by FN-f stimulated ROS and oxidized at specific cysteine residues generating cysteine sulfenic acids. Using chemical and molecular inhibitors of different oxidases and Rho family proteins, we will investigate the enzymatic source of ROS and the proteins involved in translating the integrin signal to activate ROS production in chondrocytes. This proposed work will also determine the protein target(s) of ROS that are regulated by cysteine sulfenic acid formation within the a5[unreadable]1 integrin pathway utilizing mass spectrometry, mutational protein analysis, and a specific sulfenic acid-labeling reagent called dimedone. The results of these studies will help to explain the mechanism by which excessive ROS production can lead to an imbalance in cartilage homeostasis and increased ECM degradation in the development of OA. Osteoarthritis, an age-related disease, is the most common type of arthritis in the United States and is predicted to affect approximately 60 million Americans by 2020. The proposed research will elucidate the role of reactive oxygen species in promoting cartilage breakdown in osteoarthritic joints. The results of these studies could help in the identification of potential therapeutic targets that can slow or stop cartilage loss in osteoarthritis patients.